This invention relates to tamper-evident multilayer plastic packaging films and to a tamper-evident package seal made therefrom using an adhesive cold seal.
In the past, in the packaging of certain types of food, for example, candy bars, which require packaging sealed with a cold adhesive, a sealed package is capable of being opened and subsequently put back together without evidence of tampering. The present invention remedies this problem. A tamper-evident packaging film and seal such as that of the present invention can not be resealed once the seal has been opened.
U.S. Pat. No. 4,429,015 to Sheptak discloses a multiply laminate for identification cards. Attempts to delaminate the card results in fibers being torn from a uniaxially oriented polyethylene or polypropylene layer of the laminate.
U.S. Pat. No. 4,121,003 to Williams discloses switch-proof labels using a laminate having a pattern printed on the label inner surface and a coating of pressure sensitive adhesive film on the inner surface. Attempts to transfer the label result in disruption of the printed pattern.
Neither the Williams nor Sheptak laminate is suitable for food packaging.
U.S. Pat. No. 4,632,869, the contents of which are incorporated by reference herein, discloses an opaque, biaxially oriented polymeric film structure with a thermoplastic polymer matrix core layer possessing a stratum of voids a substantial number of which contain at least one spherical void-initiating solid particle of polybutylene terephthalate, and a void-free thermoplastic skin layer on at least one surface thereof.
U.S. Pat. No. 4,377,616, the contents of which are incorporated by reference herein, discloses a lustrous, opaque biaxially oriented polymer laminate film structure comprising a thermoplastic polymer matrix core layer possessing numerous voids, a substantial number of which contain at least one void-initiating article, and transparent skin layers adhering to the surfaces of the core layer. The skin layers are of a thickness to cover surface irregularities inherent in a cavitated core layer. The structure of the core layer imparts a much higher degree of opacity than that imparted by the use of opacifying pigment alone, due to the effects of light scattering.
These opaque biaxially oriented polymer laminate structures have been used to provide films with low water vapor and gas transmission rate and pleasing appearance.
A plastic film having all these desirable characteristics and also having a tamper-evident property is much desired.
It is an object of the present invention to provide a tamper-evident packaging seal utilizing a film structure which provides a tamper-evident property to a package seal.
This tamper-evident packaging film can be sealed with heat or cold seals. Opening of the seal will result in irreversible tearing of the film so that the package cannot be resealed without evidence of tampering.